Several studies found that the fossil phase of a system could be transitional. Galaxy clusters and groups pass through fossil and non-fossil phases along their evolution. [1]} found a population of groups that presented a fossil phase at high redshift which is terminated later by the accretion of new bright galaxies. The transitional phase of the fossil status is also reported by other simulations like [2]}. This fluctuations in the magnitude gap could be related with the large-scale environment in which the systems are located. Indeed, Diaz-Gimenez et al. (2011) found that, in the Millenium Simulation, the environment was different for fossil and non-fossil systems with similar masses. They showed an increase in the local density profile of galaxies at \(\sim 2.5 \, r_{vir}\)  from the group centers. This increment was more noticeable in fossil than in non-fossil systems and was linked with the earlier formation time of fossil groups. We will discuss in Sect.  what is found in observations that can be linked to the transitional fossil phase.
